This invention relates generally to valves and deals more particularly with a ball valve which is intended for use primarily in high temperature service.
Valves which are used to handle steam and other high temperature fluids must be capable of sealing effectively at temperatures up to approximately 500.degree. to 550.degree. F. In addition, valves handlingcombustible fluids are often required to provide an acceptable seal under fire conditions where the valve components are exposed to extremely high temperatures. Since the types of materials which seal effectively at ordinary temperatures are destroyed by fire, it is common to provide secondary metal-to-metal seals which are activated upon destruction of the primary soft seals, as disclosed in U.S. Pat. Nos. 3,346,234 and 3,990,465. Seat arrangements of this type have suffered from undue cost and complexity, due in large part to the complicated shapes that are required and the need for precise machining operations on the seats. Furthermore, the ability of such seats to seal effectively under fire conditions is wholly dependent on the action of springs which are subject to wear and other damage, particularly after extensive use. Also, there is no means for closing off the lubricant passages in the seats to avoid presenting additional flow paths for the fluid in the event of a fire.